Radio Free Europe reported that "Prague's mayor, Bohuslav Svoboda, was quoted as saying from the scene that there were fears that 'three or so' people might still be inside the structure." While the AP was initially saying that "up to 40 people" were injured, CNN was reporting that fire officials said "at least 55 people" were hurt.

"The blast occurred in a building near the National Theater, not far from the Vltava River," Radio Free Europe said. It added that "the explosion shattered the windows of nearby buildings and was reportedly heard a kilometer away."

We'll monitor reports about the explosion and update as developments warrant.